In the case of ignition coils, for supplying with high voltage an ignition means, designed as a rule as a spark plug, of an internal combustion engine, which usually, in a housing, have a primary winding connected to a supply voltage and a secondary winding connected to the spark plug, as well as a soft magnetic core situated centrally to these, the connection of the ignition coil to the spark plug is carried out in practice via a sleeve made of insulating material, mostly of silicone rubber, which is drawn over a sort of connection piece of the ignition coil, and consequently forms a unit with the body of the ignition coil.
In order to contact the spark plug with the high voltage side of the ignition coil, as the contact means, in the sleeve there is usually a contact spring or alternatively an SAE (Society of Automotive Engineers) socket. In addition, parts of the secondary winding or a wound, longer interference-suppressing resistor may be situated in the sleeve.
Such a device of an interference-suppressing resistor, which is used for suppressing interference in the region of the high voltage terminal that is in connection to the secondary winding, is described, for instance, in German Patent No. DE 199 27 820.
Besides interference-suppressing resistors wound as usual, which are positioned as close as possible to the spark plug, so-called interference-suppressing resistors may also be positioned in rod-type ignition coils, in this case the ohmic proportion and accordingly also the interference-suppressing function in certain frequency ranges being low. In the latter case, an additional capacitor in the primary region of the ignition coil may be necessary.
In practice, diodes are also built into the ignition coil, which are used to suppress voltage that would be created at the beginning of the dwell time or the loading time of the ignition coil at the high voltage output of the ignition coil, and may result in undesired sparks at the spark plug. Such diodes are also designated as EFU (closing spark suppression) diodes. Such EFU diodes are high voltage diodes which, for example, use the avalanche effect or the Zener effect, and are made up, for example, of a series connection of semiconductor layers or pn junctions.
From practical experience, applications are also known in which single diodes are connected in series to a composite construction and mounted, for example, on a printed-circuit board. In summation, the respective reverse voltages of such serially connected diodes make up one high voltage diode.
The positioning of a diode may, in principle, take place on the low voltage side of the ignition coil, between the secondary winding and vehicle electrical system ground or vehicle electrical system plus, the diode also being designated as a “cold” diode; however, the diode may also be positioned on the high voltage side, between the secondary winding and the spark plug contacting as a so-called “hot” diode. For manufacturing reasons, in practice the low voltage side positioning of the diode is usually selected, although it is electrically less effective, since a diode positioned on the low voltage side permits a higher turn-on voltage than a diode positioned on the high voltage side.
Consequently, often the closing spark suppression function of a diode positioned on the low voltage side is not sufficient for ignition coils having a very rapid current rise, as are used, for example, in multi-spark systems and a 42 V vehicle electrical system.
Placing the diode on the low voltage side of the ignition coil is also problematical for reasons of space, since especially in the case of rod-type ignition coils the available space is very limited, and the diode gets in the way there.
In addition, the problem arises, in the case of positioning the diode on the low voltage side, that during operation, a reverse voltage of several thousand Volt is present at the diode, which is disadvantageous in the region of the primary plug, since in this region there is an increasing number of electronic components which are mostly mounted on printed-circuit boards. Consequently, in the available space in this region that is low anyhow, insulation distances still have to be observed in addition. A possibly interfering influence by high voltage pulses at the diode also has to be taken into consideration.
The ignition coils available in the trade show that mostly only one type of diode is applied for different types of ignition coil, which, to be sure, makes cost reduction achievable, but does not lead to a dimensioning of the diode that is adapted to the respective requirements. Therefore, in many cases the EFU diode is overdimensioned or not sufficiently dimensioned.
The same applies to interference-preventing resistors which, with respect to their resistance value, cannot be simply adapted to the requirements that are actually only able to be tested on the finished ignition coil. A subsequent change in the resistance value is connected with great expenditure, not the least being that the interference-preventing effect has to be ascertained empirically, possibly even on the vehicle.
In the case of known ignition coils, since the exchangeability of the diodes and resistors is extremely difficult, as a rule, the whole ignition coil is scrapped when a diode or a resistor fails on manufacturing final inspection.
It is therefore an object of the present invention to create an ignition coil, having a connecting device for contacting a spark plug of an internal combustion engine, using which the positioning of diodes and/or resistors adjusted to the requirements is able to be carried out in a constructively simple manner.